Add Log overloads for logging exceptions without giving a block

[lachlan]

Per the discussion on #15221 and #15253, this change provides non-yielding overloads to the Log.{{severity}} methods for logging exceptions without giving an associated message producing block:

# previously a block was required to log a bare exception without a 
# message, like so:
Log.error(exception: ex) { "" }

# this change provides non-yielding overloads to log bare exceptions 
# without requiring an empty block, which is a little easier for this 
# use case:
Log.error(exception: ex)